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<title>Arrays</title>
<body bgcolor="#ffffcc">
<hr>
<center>
<h1>Arrays.</h1>
</center>
<hr>
Arrays can be created from any of the C data types
<a href="data_types.html#int">int</a>,
<a href="data_types.html#float">float</a>,
<a href="data_types.html#char">char</a>. I start with <b>int</b> and
<b>float</b>
as these are the easiest to understand. Then move onto <b>int</b>
and <b>float</b>
multi dimentional arrays and finally <b>char</b> arrays
<ul>
<li><a href=#int><b>int</b> or <b>float</b> arrays.</a>
<li><a href=#twod>two dimensional <b>int</b> or <b>float</b> arrays.</a>
<li><a href=#char><b>char</b> arrays.</a>
<li><a href=#chard><b>char</b> multidimentional arrays.</a>
</ul>
<a name="int">
<hr>
<h2>int and float arrays</h2>
To <a href="../glossary.html#definition">define</a> an integer or
floating point variable you would say.
<pre>
main()
{
int Count; /* integer variable */
float Miles; /* floating point variable */
}
</pre>
The syntax for an array is:
<pre>
main()
{
int Count[5]; /* 5 element integer array */
float Miles[10]; /* 10 element floating point array */
}
</pre>
Now, the <b>important</b> fact is that the elements start at 0 (ZERO), so,
'Count' above has elements 0, 1, 2, 3, 4. <p>
To change the value of the 5th element we would code:
<pre>
main()
{
int Count[5];
Count[4] = 20; /* code 4 to update the 5th element */
}
</pre>
If we want to initalise 'Count' at <A HREF="../glossary.html#definition">definition</A> we can say:
<pre>
main()
{
int i;
int Count[5]={10, 20, 30};
for (i=0; i< 5; i++)
{
printf("%d ", Count[i]);
}
puts("");
}
</pre>
The result will be:
<pre>
10 20 30 0 0
</pre>
We can see from the example above that the elements that have NOT been
initalised
have been set to zero.<p>
One last thing to show you. If all the elements are being
initialized when the variable is being defined, the compiler can work out
the number of elements for you. So this example will create an array
with 3 elements.
<pre>
main()
{
int i;
int Count[]={10, 20, 30};
}
</pre>
Don't forget, all the stuff so far also applies to <b>float</b>.
<p>
<a name="twod">
<hr>
<h2>Two dimensional <b>int</b> and <b>float</b> arrays.</h2>
C does not actually support multi-dimensional arrays, but you can
emulate them.
<pre>
main()
{
int Count[5];
int Matrix[10][4];
}
</pre>
<b>Count</b> has been seen before, it defines an array of 5 elements.<p>
<b>Matrix</b> is defined as 10 arrays, all with 4 elements.<p>
To initalise <b>Matrix</b> at definition, you would code the following.
<pre>
main()
{
int Matrix[4][2]={{1, 2},
{3, 4},
{5, 6},
{7, 8}};
}
</pre>
Dont forget the last element will be <b>Matrix[3][1]</b>
<p>
<a name="char">
<hr>
<h2>char arrays.</h2>
<b>char</b> arrays work in the same way as <b>int</b> and <b>float</b>
<pre>
main()
{
char Letter;
char Letters[10];
}
</pre>
'Letter' can only hold one character but 'the 'Letters' array could hold 10.
It is important to think of 'char' as an array and NOT a string.<p>
To initalise 'char' variables you can use the following syntax.
<pre>
main()
{
char Letter='x';
char Letters[10]='f','a','x',' ','m','o','d','e','m','\0';
char Text[10]="fax modem";
}
</pre>
Note that the double quotes mean 'text string' and so they will add the
<a href=../SYNTAX/null.html>NULL</a>
automatically. This is the only time that text can be loaded into an array
in this way. If you want to change the contents of the array you should use
the function <a href=../FUNCTIONS/strcpy.html>strcpy</a>.
<p>
<a name="chard">
<hr>
<h2>Two dimensional char arrays.</h2>
Two dimensional arrays are a different kettle of fish! We can follow the
rules above to define the array like this.
<pre>
main()
{
char Colours[3][6]={"red","green","blue"};
printf ("%c \n", Colours[0][0]); /* O/P 'r' */
printf ("%s \n", Colours[1]); /* O/P 'green' */
}
</pre>
The example above has reserved 18 consecutive bytes and created three
pointers into them.
<pre>
---------------------
|red \0green\0blue \0|
---------------------
A A A
| | |
Colours[0] ---- | |
Colours[1] ----------- |
Colours[2] ------------------
</pre>
<center>
<p>
<font size= +2>
<a href=pointers.html>click here</a> for chat on pointers.
</font>
</center>
<p>
<hr>
<p>
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<p>
<hr>
<address>Martin Leslie
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